1. Field of the Invention
The present invention relates to a shaft lock device for a hinge mechanism with a rotational shaft, and to a portable information processing apparatus provided with the shaft lock device.
2. Description of the Related Art
Presently, in the field of personal computers or word processors, desktop apparatuses are being replaced by laptop apparatuses that are small, light, and portable.
As disclosed in U.S. Pat. No. 4,864,523, laptop type information processing apparatuses generally comprise a main body, which contains a keyboard, a disk drive, etc., and a display unit pivotably supported on the main body by means of a hinge mechanism.
The hinge mechanism has a shaft lock device for locking the display unit at a desired angular position. The lock device comprises a metal rotational shaft supported so as to rotate in response to the pivoting motion of the display unit, and a coil spring rigidly wound around the rotational shaft and having one end fixed to the main body of the apparatus. One end of the shaft is engaged with a first bracket of the display unit so that the shaft rotates along with the display unit. The other end of the shaft is rotatably supported by a second bracket attached to the main body. One end of the coil spring is fixed to the second bracket. The operation of the lock device with the above-mentioned structure is disclosed, e.g., in U.S. Pat. No. 3,064,766.
With the conventional shaft lock device, the coil spring with a predetermined length is wound around the rotational shaft, and the shaft is fixed at its one end to the first bracket of the display unit and is rotatably supported at its other end by the second bracket of the main body. Therefore, the entire length of the lock device is always larger than that of the coil spring. Further, for the mechanical strength of the device, the rotational shaft should be made of a metal, thus increasing the weight of the device.